Active Battery Balance

Cosun Affordable Active Cell Balance Technique

A nominal lithium cell is rated for around 3.2V only, but in its applications like EV, portable electronics, laptops, power banks etc we require a lot higher voltage than its nominal voltage. This is the reason why designers combine more than one cell in series to form a battery pack of higher voltage values. when batteries are combined in series the voltage value gets added up. For example when four lithium cells of 3.2V is connected in series the effective output voltage of the resulting battery pack will be 12.8V.

But you can imagine connecting many cells in series is like mounting many horses to a chariot. Only if all the horses run at the same speed the chariot will be driven with maximum efficiency. Out of four horses if one horse runs slowly, then the other three also has to reduce their speed thus reducing the efficiency and if one horse runs faster it would eventually hurt itself by pulling the load of the other three horses. Similarly, when four cells are connected in series the voltage values of all the four cells should be equal to derive the battery pack with maximum efficiency. The method of maintaining all the cell voltages to be equal is called as cell balancing. 

Types of Battery Cell Balancing

Cell balancing techniques can be broadly classified into the following the four categories which are listed below. We will discuss about each category.

Passive Cell Balancing VS Active Cell Balancing

1. Passive Cell Balancing

2. Active Cell Balancing

Passive cell balancing method is the simplest method of all.
It can be used in places where cost and size are major
constraints. The following are the two types of passive cell balancing.

Charge Shunting

In this method a dummy load like a resistor is used to
discharge the excess voltage and equalize it with other
 These resistors are called as bypass resistors or
bleeding resistors. Each cell connected in series in a pack
will have its own bypass resistor connected through a switch
as shown below.

In Passive cell balancing the excess charge was not
made used of, hence it is deemed to be inefficient.
Whereas in active balancing the excess charge
form one cell is transferred to another cell of
low charge to equalize them
. This is achieved by
utilizing charge storing elements like Capacitors and
Inductors. There are many methods to perform Active
cell balancing lets discuss the commonly used ones.

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